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If the roots of the equation $2x^2 - 3x + a = 0$ are in the ratio $1 : 2$, then find the value of $a$.

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
1

The problem asks us to find the value of $a$ in the quadratic equation $2x2 - 3x + a = 0$, given that its roots are in the ratio $1 : 2$.

Using Vieta's Formulas

Let the roots of the quadratic equation $Ax2 + Bx + C = 0$ be $p$ and $q$. According to Vieta's formulas:

  • Sum of roots: $p + q = -B/A$
  • Product of roots: $p * q = C/A$

In our equation, $2x2 - 3x + a = 0$, we have $A = 2$, $B = -3$, and $C = a$.

Applying the Ratio of Roots

We are given that the roots are in the ratio $1 : 2$. Let the roots be $k$ and $2k$.

Sum of roots:

$k + 2k = -(-3)/2$

$3k = 3/2$

Solving for $k$:

$k = (3/2) / 3$

$k = 1/2$

Product of roots:

$k * 2k = a/2$

$2k2 = a/2$

Calculating the Value of 'a'

Now, substitute the value of $k = 1/2$ into the product of roots equation:

$2 * (1/2)2 = a/2$

$2 * (1/4) = a/2$

$1/2 = a/2$

Multiply both sides by 2:

$a = 1$

Therefore, the value of $a$ is 1.

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